A number of industries use the flow of a slurry to achieve various purposes. In the oil well industry, for example, a mixed slurry of cement and water can be pumped downhole to support casing and isolation zones of a formation. Operators can use many types of cement mixers for these cement jobs, and the mixer can be designed to handle the particulars of the slurry to be produced, including water levels, additives, etc. Some typical mixers include jet-type mixers, vortex mixers, and continuous recirculation mixers. In other oil well applications, operators can pump a slurry of treatment fluid downhole to treat or frac the formation in the borehole. The slurry of treatment fluid can contain rock salt, wax beads, proppant (e.g., sand, ceramic beads, etc.), benzoic acid flakes, foam-based fluids, gelled and ungelled aqueous-based fluids, or other kind of material used for treating or fracing a formation. These applications can also use a mixer.
Successful cementing, fracing, and other slurry applications rely a great deal on how the slurry is mixed and pumped for its purposes. Therefore, a fundamental aspect of these operations involves knowing and controlling the density of the slurry. (For reference, cement slurry densities can range anywhere from about 7 lbm/gal [840 kg/m3] to about 23 lbm/gal [2760 kg/m3].)
In particular, oil well cementing operations require a particular density that may need to change during the cementing operation as different depths, downhole pressures, temperatures, and formations call for slurries of different densities. Depending on the application, the density of the slurry may also need to be maintained within tight tolerance and may need to change quickly during the operation. Moreover, the desired slurry may have a particular complexity that proves hard to achieve. For example, thixotropic slurries with very low “free water” requirements may be needed for deep, high temperature-high pressure gas wells. Therefore, the density of the slurry needs constant monitoring and control at the wellsite during the cementing operation.
Although several technologies exist in the art for measuring density of a slurry, current technologies used in mixing cement or fracing slurries may not accurately measure the density of the complex cement or fracing slurry. As one example, sensing technologies can measure density using coriolis sensing or nuclear sensing. Thus, one type of sensor used in measuring slurries is a nuclear densitometer. Because it uses a nuclear source, the nuclear densitometer imposes significant costs and restrictions on the movement of the equipment, and special permits and handling are required.
Even though the nuclear densitometer can be accurate, operators can use a coriolis sensor instead. Unfortunately, coriolis technology loses accuracy as more air is entrained or as particles of significantly different specific gravity are utilized together in the slurry. Additionally, a nuclear densitometer also loses accuracy as more air is entrained and is dependent on characterizing the absorption of each slurry material mix used.
Rather than using such sensors, an alternative approach in the industry measures fluid rates on the input and output sides and monitors the tub level to remain constant. This approach then back calculates the solids in the slurry by determining the volumetric difference of the slurry discharge rate and the base fluid supply rate. Historically, either the density is interpolated, or several mathematical assumptions are made to calculate density based on average flow rate.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.